[lib] Optimise owl_mac_equals()

MAC addresses are more likely to vary in the right octets than in the
left octets, so we compare them starting from the end rather than from
the beginning.

libowlps/libowlps.c

@@ -68,7 +68,7 @@ owl_bool owl_mac_equals(const uint8_t *const mac1,
                         const uint8_t *const mac2)
 {
   int i ;
-  for (i = 0 ; i < ETHER_ADDR_LEN ; ++i)
+  for (i = ETHER_ADDR_LEN - 1 ; i >= 0 ; --i)
     if(mac1[i] != mac2[i])
       return owl_false ;
   return owl_true ;